Although the magnetic insulator yttrium-iron-garnet (YIG) has been studied both experimentally and theoretically for many decades, the experimental discovery of "Bose-Einstein-condensation" of magnons in YIG at room temperature has triggered renewed interest in YIG. In my talk I describe recent theoretical efforts to understand the non-equilibrium magnon dynamics in YIG and to find a physical interpretation of room temperature "Bose-Einstein-condensation" of magnons in this material. I argue that this is a purely classical phenomenon which should be called "Rayleigh-Jeans" rather than "Bose-Einstein condensation".